Enrichment of coal‐bed methane by PSA complemented with CO₂ displacement

A PSA cycle complemented with CO 2 displacement was studied for enriching coal‐bed methane (CBM). The column was first pressurized to the adsorption pressure with feed gas, and then N 2 was produced at column top in step 2. The feed gas switched to CO 2 at the end of step 2, and the adsorbed CH 4 was displaced and pushed to column top by CO 2 becoming the second column‐top product in step 3. The CO 2 stream was shut off before it broke through the sorption bed. Then bed regeneration followed. A series of CH 4 /N 2 mixtures containing 17.62 to 51.33% CH 4 was used for feed gas. It was experimentally shown that the product concentration was higher than 90%, and methane recovery was higher than 98% even for the feed of low‐methane concentration. Displacement at ambient pressure was shown more efficient than the displacement at adsorption pressure for the enrichment.